In the textile industry, the determination of the amount of the substance of fiber structures, in particular the cross-sectional substance, is very important. The cross-sectional substance of slivers is of considerable importance in the processing thereof to form yarn, because this cross-sectional substance directly influences the fineness of the yarn and the evenness of the cross-sectional regularity thereof.
Primarily, a measurement of the substance or density of a fiber quantity involves a determination of the amount of substance of a fiber structure, without taking into account whether the fiber is moving or stationary. In this regard, the measurement of moving slivers does not differ in principle from the measurement of stationary slivers, only the parts which guide and limit the slivers must be correspondingly adapted.
The determination of substance in a direct manner, such as by weighing, is practically impossible, particularly on running slivers. For this reason, different proposals for the solution of this problem have been advanced which are based on the indirect measurement of cross-sectional substance. Such proposals have involved purely mechanical measurement by means of a grooved roller and a feeler roller, the use of optical measuring devices which utilize the absorption or reflection capacity of the slivers, and acoustic measuring devices. All of these approaches have proven to be undesirable or unsatisfactory for one reason or another.
The so-called active-pneumatic measuring device must also be mentioned as another method of determining the substance cross section of slivers. This measuring device essentially comprises a funnel, to the side of which is connected a pressure measuring device. When a sliver passes through the funnel, pressure variations are caused on this lateral connection, which are transformed into equivalent signals which correspond to the cross section of the sliver. This active-pneumatic measuring device is, in itself, of simple design and very easy to install; however, it has the disadvantage that the measured values are dependent both on the fineness of the fiber (micron-air value) and on the speed of movement of the sliver.
Extensive work has also taken place to determine the elasticity of a sliver passing through a duct having defined dimensions. With this method, the sliver is regarded as a spring, which builds up a system of mechanical oscillations, together with the mass of the sliver. Thus, the resonance frequency of the system on the one hand or the transit time of oscillation pulses on the other hand produce a measure of the substance amount or density of the fibers. A process of this type and the appropriate devices for the determination of the amount of substance or the density of quantities of fibers based on the utilization of the elastic properties of the material have been described, for example, in U.S. Application Ser. No. 384,942, filed June 4, 1982. The disadvantage of this process and the related devices is the high cost of the generator, receiver and the auxiliary equipment for the determination of the amount of substance of the fiber material.